This study will contribute to the understanding of sexual differentiation (SD) and monoamine (MA) function, both of which have important clinical significance. Malfunction of SD results in serious neuroendocrine disorders in the adult. The roles that MA's play in SD are clinically important in relation to the widespread use of MA-modifying drugs in psychiatry, neurology, and mood control. The health-related consequences of exposing the fetus or neonate to these drugs through maternal use are not presently understood but are to be investigated by this project. Basically, sexual differentiation of the gonadotrophic hormone (GTH) secretion pattern is due to the action of neonatal testicular androgen on the hypothalamus in permanently suppressing the cyclic, female pattern and inducing the tonic pattern of the male. Hypothalamic monoamines (MA's) have been found to play essential roles in GTH regulation, but little is known about the functions of MA's in SD of GTH secretion pattern. Once dose levels were established, female rat pups were treated during the neonatal critical period for SD with monoamine-modifying agents, 1 to 3 doses (8, 16, and 32 mg) of testosterone proprionate (TP), vehicles for the above, or a combination of the above. Data were gathered concerning age of puberty, vaginal cyclicity, the occurrence of ovulation, and gonadotropin secretion pattern. Initially, pups will be treated with MA antagonists administered systemically. Those antagonists that did modify SD will next be administered along with repletion agents that should restore the MA's and result in normal SD. Having confirmed the identity of the MA's active in SD, their antagonists will be implanted in various loci of the hypothalamus. When the loci at which hypothalamic MA's are active in SD have been thus identified, these sites will be verified by combining hypothalamic implants of antagonists with systemic administration of repletion agents. Thus, not only will knowledge about roles of MA's in SD be advanced, the hypothalamic structures involved will be indicated.